Sensor apparatus

ABSTRACT

A sensor apparatus includes: an element substrate; a detecting section disposed on an upper surface of the element substrate, the detecting section including a reaction section having an immobilization film to detect an analyte; a first IDT electrode configured to generate an acoustic wave which propagates toward the reaction section, and a second IDT electrode configured to receive the acoustic wave which has passed through the reaction section; and a protective film located on the upper surface of the element substrate so as to cover the first IDT electrode, the second IDT electrode, and at least part of the immobilization film, the protective film extending between and contacting with the immobilization film and at least one of the first IDT electrode and the second IDT electrode.

TECHNICAL FIELD

The present invention relates to a sensor apparatus which is capable of measurement on the properties or constituents of an analyte liquid.

BACKGROUND ART

There is known a sensor apparatus which measures the properties or constituents of an analyte liquid by detecting an object to be detected contained in the analyte liquid with use of a detecting element such as a surface acoustic wave device (refer to Patent Literatures 1 to 3, for example).

For example, in a sensor apparatus employing a surface acoustic wave device, a reaction section which undergoes reaction with a component contained in a sample of an analyte liquid, is disposed on a piezoelectric substrate, and the properties or constituents of the analyte liquid are detected by measuring variation in a surface acoustic wave propagating through the reaction section. Such a measurement method using the surface acoustic wave device or the like has the advantage over other measurement methods (for example, enzymatic method) in that it lends itself to simultaneous detection of a plurality of characteristics to be measured.

However, such a conventional sensor apparatus is prone to losses of surface-acoustic-wave energy occurring at a boundary between the piezoelectric substrate and a constituent component disposed on the piezoelectric substrate, which results in difficulties in detecting an object to be detected contained in an analyte with high sensitivity.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication JP-A 5-240762 (1993)

Patent Literature 2: Japanese Unexamined Patent Publication JP-A 2006-184011

Patent Literature 3: Japanese Unexamined Patent Publication JP-A 2010-239477

SUMMARY OF INVENTION Technical Problem

Thus, there is a demand for a sensor apparatus which is capable of detecting an object to be detected contained in an analyte liquid with excellent sensitivity.

Solution to Problem

A sensor apparatus according to an embodiment of the invention includes: an element substrate; a detecting section disposed on an upper surface of the element substrate, the detecting section including a reaction section having an immobilization film to detect an analyte; a first IDT electrode configured to generate an acoustic wave which propagates toward the reaction section, and a second IDT electrode configured to receive the acoustic wave which has passed through the reaction section; and a protective film located on the upper surface of the element substrate so as to cover the first IDT electrode, the second IDT electrode, and at least part of the immobilization film, the protective film extending between and contacting with the immobilization film and at least one of the first IDT electrode and the second IDT electrode.

Advantageous Effects of Invention

In accordance with the sensor apparatus according to the embodiment of the invention, in the element substrate, the protective film located on the upper surface of the element substrate covers, in addition to the first IDT electrode and the second IDT electrode, at least part of the immobilization film, the protective film extending between and contacting with the immobilization film and at least one of the first IDT electrode and the second IDT electrode. Accordingly, it is possible to reduce losses of surface-acoustic-wave energy at a boundary between the element substrate and a constituent component disposed on the element substrate, and thereby detect an object to be detected contained in an analyte with high sensitivity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing a sensor apparatus according to an embodiment of the invention, and FIG. 1(a) is a plan view, FIG. 1(b) is a lengthwise sectional view, and FIG. 1(c) is a widthwise sectional view;

FIG. 2 is an exploded plan view of the sensor apparatus shown in FIG. 1;

FIG. 3 is a plan view showing procedural steps to manufacture the sensor apparatus shown in FIG. 1;

FIG. 4 is a plan view showing a detecting element of the sensor apparatus shown in FIG. 1;

FIG. 5 is a sectional view showing the detecting element of the sensor apparatus shown in FIG. 1;

FIG. 6 is an enlarged sectional view showing part of the sensor apparatus shown in FIG. 5; and

FIG. 7 is a schematic view showing procedural steps to manufacture the detecting element 3.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of a sensor apparatus according to the invention will be described with reference to drawings. In each drawing to be referred to in the following description, like constituent members are identified with the same reference symbols. Moreover, for example, the size of each member and the distance between the individual members are schematically shown in each drawing and may therefore differ from the actual measurements.

<Structure of Sensor Apparatus>

A sensor apparatus 100 according to an embodiment of the invention will be described with reference to FIGS. 1 to 6.

As shown in FIG. 1, the sensor apparatus 100 according to the embodiment mainly comprises a first cover member 1, an intermediate cover member 1A, a second cover member 2, and a detecting element 3.

Specifically, as shown in FIG. 1(b), the sensor apparatus 100 has an inlet port 14 for admission of an analyte liquid, and a flow channel 15 which is in communication with the inlet port 14, is surrounded by the intermediate cover member 1A and the second cover member 2, and extends at least to a reaction section 13. In this embodiment, the intermediate cover member 1A and the second cover member 2 are greater in width than the detecting element 3. This allows an analyte liquid to flow so as to cover the entire surface of the detecting element 3 effectively.

FIG. 1(c) which shows sectional views of the construction shown in FIG. 1(a), wherein there are successively shown, in top-to-bottom order, a section taken along the line a-a, a section taken along the line b-b, and a section taken along the line c-c. The inlet port 14 is formed so as to pass through the second cover member 2 in a thickness direction thereof.

(First Cover Member 1)

As shown in FIGS. 1(a), 1(b) and FIG. 2(a), the first cover member 1 is shaped like a flat plate. The thickness of the first cover member 1 falls in the range of 0.1 mm to 1.5 mm, for example. The first cover member 1 has substantially a rectangular planar configuration. The longitudinal length of the first cover member 1 falls in the range of 1 cm to 8 cm, for example, and, the widthwise length of the first cover member 1 falls in the range of 1 cm to 3 cm, for example.

As the material for forming the first cover member 1, for example, a glass-epoxy material, paper, plastics, celluloid, ceramics, non-woven fabric, and glass can be used. The use of plastics is desirable from the standpoints of required strength and cost.

Moreover, as shown in FIGS. 1(a) and 2(a), on the upper surface of the first cover member 1 are formed a terminal 6 and a wiring line 7 routed from the terminal 6 to a position near the detecting element 3.

The terminal 6 is formed on either side of the detecting element 3 in a width direction on the upper surface of the intermediate cover member 1A. Specifically, at least part of the terminals 6 arranged relative to the detecting element 3 lies closer to the inlet port 14 than an inlet port 14-side end of the detecting element 3. Moreover, in the range of four terminals 6 placed in an array on one side of the detecting element 3 with respect to a direction longitudinally of the flow channel 15, the wiring lines 7 connected to two outer terminals 6, respectively, have substantially the same length, and, the wiring lines 7 connected to the other two inner terminals 6, respectively, have substantially the same length. This makes it possible to reduce variations in signals obtained by the detecting element 3 resulting from the difference in length between the wiring lines 7. In this case, with a construction in which the wiring lines 7 are connected so that a potential difference occurs between grounding (earthing) wiring, which is constituted by one pair of the wiring lines 7 having substantially the same length, and signal wiring, which is constituted by the other pair of the wiring lines 7 having substantially the same length, for example, upon application of a predetermined voltage from external measurement equipment to a first IDT electrode 11 as shown in FIG. 4 via the wiring line 7, a first extraction electrode 19, and so forth, it is possible to reduce the signal variations, and thereby achieve an improvement in detection reliability.

When measurement is made on the sensor apparatus 100 with external measuring equipment (not shown in the drawing), the terminal 6 and the external measuring equipment are electrically connected to each other. Moreover, the terminal 6 and the detecting element 3 are electrically connected to each other via the wiring line 7, for example.

A signal issued from the external measuring equipment is inputted to the sensor apparatus 100 via the terminal 6, and, a signal issued from the sensor apparatus 100 is outputted to the external measuring equipment via the terminal 6.

(Intermediate Cover Member 1A)

In this embodiment, as shown in FIG. 1(b), the intermediate cover member 1A is placed in juxtaposition to the detecting element 3 on the upper surface of the first cover member 1. Moreover, as shown in FIGS. 1(a) and 3(c), the intermediate cover member 1A and the detecting element 3 are arranged with a spacing. Note that the intermediate cover member 1A and the detecting element 3 may be arranged with their sides kept in contact with each other.

As shown in FIGS. 1(b) and 2(b), the intermediate cover member 1A has the form of a flat frame constructed of a flat plate having a recess-forming area 4, and, the thickness of the intermediate cover member 1A falls in the range of 0.1 mm to 0.5 mm, for example.

In this embodiment, as shown in FIG. 1(b), the recess-forming area 4 is an area located downstream of a first upstream portion 1Aa. The intermediate cover member 1A is joined to the flat plate-shaped first cover member 1, whereupon an element placement section 5 is defined by the first cover member 1 and the intermediate cover member 1A. That is, the upper surface of the first cover member 1 located inside the recess-forming area 4 becomes the bottom surface of the element placement section 5, and, the inner wall of the recess-forming area 4 becomes the inner wall of the element placement section 5.

As shown in FIGS. 1 and 3, in a region located downstream of the detecting element 3, the intermediate cover member 1A does not exist on the first cover member 1. This makes it possible to inhibit or reduce generation of bubbles in a part of the intermediate cover member 1A located downstream of the first upstream portion 1Aa. In consequence, an analyte liquid can be delivered in a bubble-free state onto the detecting element 3, thus achieving an improvement in sensitivity or accuracy in detection.

As the material for forming the intermediate cover member 1A, for example, resin (including plastics), paper, non-woven fabric, and glass can be used. More specifically, resin materials such as polyester resin, polyethylene resin, acrylic resin, and silicone resin are desirable for use. The first cover member 1 and the intermediate cover member 1A may be formed of either the same material or different materials.

Moreover, in this embodiment, the intermediate cover member 1A includes the first upstream portion 1Aa. As shown in FIGS. 1(a) and 1(b), when viewed from above, the detecting element 3 is located on the downstream side relative to the first upstream portion 1Aa. In this case, when an analyte liquid flows out over the detecting element 3 after passing through a part of the flow channel 15 which corresponds to the first upstream portion 1Aa, an excess of the analyte liquid over an amount of the analyte liquid required for measurement flows downstream, wherefore an adequate amount of the analyte liquid can be fed to the detecting element 3.

(Second Cover Member 2)

As shown in FIGS. 1(b) and 3(e), the second cover member 2 covers the detecting element 3, and is joined to the first cover member 1 and the intermediate cover member 1A. As shown in FIGS. 1(b) and 1(c), the second cover member 2 comprises a third substrate 2 a and a fourth substrate 2 b.

As the material for forming the second cover member 2, for example, resin (including plastics), paper, non-woven fabric, and glass can be used. More specifically, resin materials such as polyester resin, polyethylene resin, acrylic resin, and silicone resin are desirable for use. The first cover member 1 and the second cover member 2 may be formed of the same material. In this case, deformation resulting from the difference in thermal expansion coefficient between the first and second cover members can be minimized. The second cover member 2 may either be joined only to the intermediate cover member 1A or be joined to both of the first cover member 1 and the intermediate cover member 1A.

As shown in FIGS. 1(c), 3(c), and 3(d), the third substrate 2 a is bonded to the upper surface of the intermediate cover member 1A. The third substrate 2 a is shaped like a flat plate having a thickness of 0.1 mm to 0.5 mm, for example. The fourth substrate 2 b is bonded to the upper surface of the third substrate 2 a. The fourth substrate 2 b is shaped like a flat plate having a thickness of 0.1 mm to 0.5 mm, for example. By joining the fourth substrate 2 b to the third substrate 2 a, as shown in FIG. 1(b), the flow channel 15 is formed on the lower surface of the second cover member 2. The flow channel 15 extends from the inlet port 14 to at least a region immediately above the reaction section 13, and has a rectangular sectional profile, for example. The third substrate 2 a and the fourth substrate 2 b may be formed of the same material, or, an unitary construction of the combined third and fourth substrates 2 a and 2 b may be used.

In this embodiment, as shown in FIG. 1(b), neither the intermediate cover member 1A nor the third substrate 2 a exists at an end of the flow channel 15, and, a gap left between the fourth substrate 2 b and the first cover member 1 serves as an air release hole 18. The air release hole 18 is provided to let air and so forth present in the flow channel 15 go out. The opening of the air release hole 18 may be given any shape which is capable of release of air present in the flow channel 15, and thus, for example, a circular shape or a rectangular shape may be adopted. For example, in the case of an air release hole 18 having a circular opening, the opening is designed to have a diameter of less than or equal to 2 mm, and, in the case of an air release hole 18 having a rectangular shape, the air release hole 18 is designed so that each side of the rectangle has a length of less than or equal to 2 mm.

The first cover member 1, the intermediate cover member 1A, and the second cover member 2 may be formed of the same material. In this case, since these members are substantially uniform in thermal expansion coefficient, it is possible to reduce deformation of the sensor apparatus 100 caused by the difference in thermal expansion coefficient among the members. Moreover, in the case of application of a biomaterial to the reaction section 13, some biomaterials are prone to quality degradation under external light such as ultraviolet rays. In this regard, it is advisable to use an opaque material having light-blocking capability as the material for forming the first cover member 1, the intermediate cover member 1A, and the second cover member 2. On the other hand, when the reaction section 13 is substantially free of external light-induced quality degradation, the second cover member 2 constituting the flow channel 15 may be formed of a nearly transparent material. In this case, the condition of an analyte liquid flowing through the interior of the flow channel 15 can be visually checked, thus permitting the combined use of an optical detection system.

(Detecting Element 3)

The detecting element 3 in the present embodiment will be described with reference to FIGS. 1 to 6, in particular, FIGS. 4 to 6.

FIG. 6 is an enlarged sectional view showing part of the sensor apparatus shown in FIG. 5, and more specifically FIG. 6(a) is an enlarged view of the principal portion of the detecting element shown in FIG. 5(b), and FIG. 6(b) is an enlarged view of part of the principal portion shown in FIG. 6(a).

As shown in FIG. 6, the detecting element 3 generally comprises an element substrate 10 a disposed on the upper surface of the first cover member 1, and at least one detecting section 10 b, disposed on the upper surface of the element substrate 10 a, for detecting an object to be detected (detection target) contained in an analyte liquid.

Specifically, as shown in FIG. 6, the detecting element 3 in this embodiment comprises: the element substrate 10 a; the detecting section 10 b disposed on the upper surface of the element substrate 10 a, the detecting section 10 b including the reaction section 13 having an immobilization film 13 a to detect an object to be detected, a first IDT (InterDigital Transducer) electrode 11 configured to generate an acoustic wave which propagates toward the reaction section 13, and a second IDT electrode 12 configured to receive the acoustic wave which has passed through the reaction section 13; and a protective film 28 located on the upper surface of the element substrate 10 a so as to cover the first IDT electrode 11, the second IDT electrode 12, and at least part of the immobilization film 13 a, the protective film 28 extending between and contacting with the immobilization film 13 a and at least one of the first IDT electrode 11 and the second IDT electrode 12.

The detecting section 10 b includes, in addition to the first IDT electrode 11, the reaction section 13, and the second IDT electrode 12, the protective film 28, a first extraction electrode 19, a second extraction electrode 20, and so forth.

(Element Substrate 10 a)

The element substrate 10 a is constructed of a substrate of single crystal having piezoelectric properties such for example as quartz, lithium tantalate (LiTaO₃) single crystal, or lithium niobate (LiNbO₃) single crystal. The planar configuration and dimensions of the element substrate 10 a are suitably determined. The element substrate 10 a has a thickness of 0.3 mm to 1 mm, for example.

In this embodiment, a surface roughness of the upper surface of the immobilization film 13 a is greater than a surface roughness of a region where the immobilization film 13 a is located in the element substrate 10 a. In this case, for example, in immobilizing aptamers and antibodies, which will hereafter be described, onto the surface of the element substrate 10 a, it is possible to increase bindability of the aptamers and antibodies to the surface of the immobilization film 13 a, thus enabling high-density immobilization. This makes it possible to improve detection sensitivity of the object to be detected.

(IDT Electrodes 11 and 12)

As shown in FIGS. 4 and 6, the first IDT electrode 11 comprises a pair of comb electrodes. Each comb electrode includes two bus bars opposed to each other and a plurality of electrode fingers 11 a to 11 e (11 a, 11 b, 11 c, 11 d, and 11 e) each extending from corresponding one of the bus bars toward the other. A pair of the comb electrodes is disposed so that the plurality of electrode fingers 11 a to 11 e are arranged in an interdigitated pattern. The second IDT electrode 12 is similar in configuration to the first IDT electrode 11. The first IDT electrode 11 and the second IDT electrode 12 constitute a transversal IDT electrode.

The first IDT electrode 11 is intended for generation of predetermined surface acoustic wave (SAW), and the second IDT electrode 12 is intended for reception of the SAW generated in the first IDT electrode 11. The first IDT electrode 11 and the second IDT electrode 12 are positioned on the same straight line so that the SAW generated in the first IDT electrode 11 can be received by the second IDT electrode 12. Frequency response characteristics can be designed on the basis of the number of the electrode fingers of the first IDT electrode 11 and the second IDT electrode 12, the distance between the adjacent electrode fingers, the crossing width of the electrode fingers, etc., used as parameters.

There are various modes of vibration for SAW to be excited by the IDT electrode. In the detecting element 3 according to the embodiment, for example, a vibration mode of transversal waves called SH waves is utilized. The frequency of SAW may be set within the range of several megahertz (MHz) to several gigahertz (GHz), for example. It is advisable to set the SAW frequency within the range of several hundred MHz to 2 GHz from the practicality standpoint, and also in the interest of miniaturization of the detecting element 3 that will eventually be conducive to miniaturization of the sensor apparatus 100. The thicknesses and lengths of predetermined constituent elements in the embodiment will be described with respect to the case where the center frequency of SAW falls in a several hundred MHz range.

The first IDT electrode 11 and the second IDT electrode 12 may be of a single-layer structure composed of, for example, a gold thin layer, or may be of a multilayer structure such as a three-layer structure composed of a titanium layer, a gold layer, and a titanium layer, or a three-layer structure composed of a chromium layer, a gold layer, and a chromium layer, in the order, named, from the element-substrate 10 a side.

A thickness of the first IDT electrode 11 and the second IDT electrode 12 may be set to fall within the range of 0.005λ to 0.015λ, for example.

An elastic member may be disposed externally of the first IDT electrode 11 and the second IDT electrode 12 in a SAW propagation direction (width direction) to reduce SAW reflection.

(Reaction Section 13)

As shown in FIGS. 4 and 6, the reaction section 13 is disposed between the first IDT electrode 11 and the second IDT electrode 12.

In this embodiment, the reaction section 13 comprises the immobilization film 13 a (for example, a metallic film) formed on the upper surface of the element substrate 10 a, and a reactant immobilized on the upper surface of the immobilization film 13 a for reaction with an object to be detected. The reactant is suitably selected depending on an object to be detected which is a detection target. For example, when the object to be detected is a specific cell or living tissue present in an analyte liquid, an aptamer composed of a nucleic acid or a peptide can be used as the reactant. For example, in this embodiment, while a reaction between the reactant and the object to be detected may be a binding reaction of the object to be detected and the reactant such as a chemical reaction or an antigen-antibody reaction, the reaction is not so limited, but may be a binding reaction of the object to be detected and the reactant under the interaction of the object to be detected with the reactant, or an adsorption reaction of the object to be detected to the reactant. Exemplary of a reactant which can be used for the reaction section 13 in the embodiment is one which causes, by its presence, variation in surface-acoustic-wave characteristics according to the type or content of the object to be detected when an analyte is brought into contact with the reaction section 13. The reaction section 13 is intended for causing reaction with an object to be detected contained in an analyte liquid, and, more specifically, upon contact of an analyte liquid with the reaction section 13, a specific object to be detected contained in the analyte liquid is bound to an aptamer adapted to the object to be detected.

The immobilization film 13 a (metallic film) may be of a single-layer structure composed of, for example, a gold layer, or may be of a multilayer structure such as a two-layer structure composed of a titanium layer and a gold layer situated on the titanium layer or a two-layer structure composed of a chromium layer and a gold layer situated on the chromium layer. Moreover, the immobilization film 13 a may be formed of the same material as a material used for the first IDT electrode 11 and the second IDT electrode 12. In this case, the immobilization film 13 a and the first and second IDT electrodes 11 and 12 can be formed in the same process step. Instead of the above-mentioned metallic film, for example, an oxide film such as a SiO₂ film or TiO₂ film may be used as the material of construction of the immobilization film 13 a.

Given that the first IDT electrode 11, the second IDT electrode 12, and the reaction section 13 arranged in the width direction of the flow channel are grouped into a set, then, as shown in FIG. 4, two sets are provided in the sensor apparatus 100 according to the embodiment. In this case, by designing the reaction section 13 of one of the sets and the reaction section 13 of the other to undergo reaction with different detection targets, it is possible to detect two different objects to be detected by a single sensor apparatus.

In this embodiment, as shown in FIG. 6, the upper surface of the immobilization film 13 a comprises regions 13 a 1 which are covered with the protective film 28 and are at ends of the side of the first IDT electrode 11 and the side of the second IDT electrode 12, respectively, and a region 13 a 2 of a center part which is not covered with the protective film 28. An upper surface of the region 13 a 1 which is covered with the protective film 28 is at a higher level than an upper surface of the region 13 a 2 which is not covered with the protective film 28. In this case, in the reaction section 13, energy of SAW propagating between the first IDT electrode 11 and the second IDT electrode 12 tends to be further concentrated on the upper surface of the region 13 a 2 which is not covered with the protective film 28 in the upper surface of the immobilization film 13 a, wherefore an object to be detected can be detected with high sensitivity. As a specific example, as shown in FIG. 6(b), the upper surface of the immobilization film 13 a may be so inclined that a level of the upper surface becomes lower as approaching from the region 13 a 1 which is covered with the protective film 28 to the region 13 a 2 which is not covered with the protective film 28.

In this embodiment, as shown in FIG. 6(b), the upper surface of the region 13 a 1 which is covered with the protective film 28 in the upper surface of the immobilization film 13 a is at substantially the same level as at least one of the upper surface of the first IDT electrode 11 and the upper surface of the second IDT electrode 12. This makes it possible to reduce losses of energy when SAW propagating through the element substrate 10 a is transmitted from the first IDT electrode 11 via the immobilization film 13 a to the second IDT electrode 12.

Moreover, the upper surface of the region 13 a 2 which is not covered with the protective film 28 in the upper surface of the immobilization film 13 a is at a lower level than at least one of the upper surface of the first IDT electrode 11 and the upper surface of the second IDT electrode 12. In this case, in the reaction section 13, energy of SAW propagating between the first IDT electrode 11 and the second IDT electrode 12 tends to be concentrated on the upper surface of the immobilization film 13 a, wherefore an object to be detected can be detected with even higher sensitivity.

In this embodiment, as shown in FIG. 6(b), a thickness of the region 13 a 1 which is covered with the protective film 28 of the immobilization film 13 a is greater than a thickness of the region 13 a 2 which is not covered with the protective film 28 thereof. In the immobilization film 13 a, given that the wavelength of SAW propagating between the first IDT electrode 11 and the second IDT electrode 12 is λ, then a thickness of the region 13 a 1 which is covered with the protective film 28 may be set to fall within, for example, the range of 0.005λ to 0.015λ, and, for example, and a thickness of the region 13 a 2 which is not covered with the protective film 28 may be set to be 0.01λ or below smaller than the thickness of the region 13 a 1 which is covered with the protective film 28, and may thus be set to fall within the range of 0.004λ to 0.014λ. In this case, even if the region 13 a 2 which is not covered with the protective film 28 of the immobilization film 13 a has a relatively small thickness, in the reaction section 13, losses of energy of SAW propagating between the first IDT electrode 11 and the second IDT electrode 12 can be reduced. In addition to that, since the SAW energy tends to be concentrated on the upper surface of the region 13 a 2 which is not covered with the protective film 28 of the immobilization film 13 a, it is possible to detect an object to be detected with even higher sensitivity. As a specific example, as shown in FIG. 6(b), the immobilization film 13 a may be so shaped that its thickness becomes smaller as approaching from the region 13 a 1 which is covered with the protective film 28 to the region 13 a 2 which is not covered with the protective film 28.

In this embodiment, the surface roughness of the upper surface of the region 13 a 2 which is not covered with the protective film 28 in the upper surface of the immobilization film 13 a is greater than the surface roughness of the upper surface of the first IDT electrode 11 and the surface roughness of the upper surface of the second IDT electrode 12. In this case, since the surface area of the immobilization film 13 a can be increased, it is possible to immobilize reactants such as aptamers and antibodies onto the immobilization film 13 a at high densities, and thereby improve detection sensitivity of the object to be detected. a surface roughness of the upper surface of the region 13 a 2 which is not covered with the protective film 28 in the upper surface of the immobilization film 13 a may be set to fall within the range of 2.0 to 10.0 nm, for example, in terms of arithmetic average roughness Ra. The surface roughness of each constituent element may be determined by measurement using arithmetic average roughness Ra. In the case where a film or the like is disposed on a measurement target, for example, graphic analyses of the sectional profile of the measurement target are performed on the basis of a photograph of the section obtained by means of SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy), or otherwise, for surface roughness measurement. Moreover, when direct measurement of the measurement target is possible, the measurement may be effected with use of a commonly-used surface-roughness meter of contact type or non-contact type.

Moreover, it is advisable that the surface roughness of the upper surface of the region 13 a 1 which is covered with the protective film 28 in the upper surface of the immobilization film 13 a is substantially equal to the surface roughness of the upper surface of the first IDT electrode 11 and the surface roughness of the upper surface of the second IDT electrode 12. This makes it possible to render the immobilization film 13 a, the first IDT electrode 11, and the second IDT electrode 12 uniform in bondability to the protective film 28.

(Protective Film 28)

As shown in FIG. 6, the protective film 28 is located on the upper surface of the element substrate 10 a so as to cover the first IDT electrode 11 and the second IDT electrode 12. This makes it possible to inhibit an analyte liquid from contact with the first IDT electrode 11 and the second IDT electrode 12, and thereby retard corrosion of the IDT electrodes caused by oxidation, for example. Examples of materials used for the protective film 28 include silicon oxide, aluminum oxide, zinc oxide, titanium oxide, silicon nitride, and silicon. Such a material is properly used as a major constituent, namely a component constituting the greatest proportion in mass, of a material for forming the protective film 28, and is therefore not defined as the constituent material when mixed merely as impurities in very small amounts, for example.

Moreover, in this embodiment, as shown in FIG. 6, the protective film 28 also covers at least part of the immobilization film 13 a, and extends between and contacts with the immobilization film 13 a and at least one of the first IDT electrode 11 and the second IDT electrode 12. This makes it possible to reduce losses of SAW energy at an interface between the element substrate 10 a and a constituent component disposed on the element substrate 10 a, and thereby detect an object to be detected contained in an analyte with high sensitivity. As a specific example, as shown in FIG. 6(b), the protective film 28 covers the ends of the immobilization film 13 a located on the side of the first IDT electrode 11 and the side of the second IDT electrode 12. This makes it possible to inhibit an analyte liquid from contact with the end of the immobilization film 13 a and thereby retard corrosion caused for example by oxidation, as well as to immobilize reactants such as aptamers and antibodies onto the central region 13 a 2 of the immobilization film 13 a which is not covered with the protective film 28 and thereby ensure detection sensitivity of the object to be detected.

In this embodiment, as shown in FIG. 6(b), the protective film 28 extends between and contact with the immobilization film 13 a and at least one of the first IDT electrode 11 and the second IDT electrode 12. As a specific example, as shown in FIG. 6(b), the protective film 28 is disposed so as to thoroughly fill the gap between the immobilization film 13 a and the first, second IDT electrode 11, 12 disposed on the element substrate 10 a. In this case, the interposition of the protective film 28 between the immobilization film 13 a and the first, second IDT electrode 11, 12 makes it possible to suppress acoustic impedance variation, and thereby minimize the influence of reflected waves entailed by the placement of other member, with consequent reduction in SAW energy losses.

As shown in FIGS. 4 and 6, the first IDT electrode 11 and the second IDT electrode 12 include a plurality of electrode fingers 11 a to 11 e and the plurality of electrode fingers 12 a to 12 e (12 a, 12 b, 12 c, 12 d, and 12 e) which are spaced apart from each other, respectively, and, as shown in FIG. 6(b), the protective film 28 is made in continuous (connected) form so as to 11 e over, out of the plurality of electrode fingers 11 a to 11 e, as well as 12 a to 12 e, two adjacent electrode fingers, for example, the electrode fingers 11 a and 11 b, as well as 12 a and 12 b, and also over that part of the element substrate 10 a located between the two electrode fingers 11 a and 11 b, as well as 12 a and 12 b. This makes it possible to inhibit occurrence of short-circuiting between the plurality of electrode fingers of the IDT electrode caused by an analyte liquid.

Moreover, as shown in FIG. 6(b), an end of the protective film 28 located on a side of the reaction section 13 (the immobilization film 13 a) comprises a lower end part and an upper end part, the lower end part being closer to a center part of the reaction section 13 (the immobilization film 13 a) than the upper end part when viewed in a lateral section. As used herein, the language “lateral section” means, as will be seen from FIG. 1(b) for example, a section taken along the line a-a of FIG. 1(a) or a line perpendicular to the line a-a, looking from the side of the sensor apparatus. Moreover, the language “end located on a side of the reaction section 13” means an end of the protective film 28 opposite the end located toward at least one of the first IDT electrode 11 and the second IDT electrode 12 under the condition where, for example, as described above, the protective film 28 lies also in between the reaction section 13 and at least one of the first IDT electrode 11 and the second IDT electrode 12, and does not cover the entire area of the reaction section 13. Furthermore, as shown in FIG. 6(b), an end of the protective film 28 located on the side of the reaction section 13 (the immobilization film 13 a) comprises a lower end part and an upper end part, the end being inclined so that the distance between the end and a center part of the reaction section 13 (the immobilization film 13 a) becomes shorter as the end going from the upper end part to the lower end part when viewed in a lateral section. This makes it possible to inhibit an analyte liquid from contact with the first IDT electrode 11 and the second IDT electrode 12 more effectively. Moreover, by forming the protective film 28 so as to cover the upper surface of the element substrate 10 a, it is possible to enhance stability of connection with the element substrate 10 a.

In this embodiment, a thickness of the protective film 28 may be set to fall within the range of 0.001λ to 0.05λ, for example. While the thickness of the protective film 28 may be measured in a part of the protective film 28 which covers neither the first IDT electrode 11 nor the second IDT electrode 12, the measurement in other part will not be excluded herein.

As an alternative to the configuration as shown in FIG. 6 just described, a thickness of the protective film 28 may be smaller than the thickness of the first IDT electrode 11 and the thickness of the second IDT electrode 12. This makes it possible to reduce the influence of the protective film 28 upon SAW propagating between the first IDT electrode 11 and the second IDT electrode 12, and thereby reduce losses of SAW energy. In this case, the upper surface of the protective film 28 may be, at least partly, positioned at a level lower than the upper surface of the first IDT electrode 11 and the upper surface of the second IDT electrode 12.

(Extraction Electrodes 19 and 20)

As shown in FIG. 4, the first extraction electrode 19 is connected to the first IDT electrode 11, and the second extraction electrode 20 is connected to the second IDT electrode 12. The first extraction electrode 19 is extracted from the first IDT electrode 11 in the opposite direction to the reaction section 13, and, an end 19 e of the first extraction electrode 19 is electrically connected to the wiring line 7 disposed in the first cover member 1. The second extraction electrode 20 is extracted drawn from the second IDT electrode 12 in the opposite direction to the reaction section 13, and, an end 20 e of the second extraction electrode 20 is electrically connected to the wiring line 7.

The first extraction electrode 19 and the second extraction electrode 20 may be made similar in material and configuration to the first IDT electrode 11 and the second IDT electrode 12, and may thus be of a single-layer structure composed of, for example, a gold thin layer, or may be of a multilayer structure such as a three-layer structure composed of a titanium layer, a gold layer, and a titanium layer, or a three-layer structure composed of a chromium layer, a gold layer, and a chromium layer, in the order named, from the element-substrate 10 a side.

(Detection of Detection Target Using Detecting Element 3)

In the process of detection of an object to be detected contained in an analyte liquid by the detecting element 3 that utilizes SAW as above described, the first step is to apply a predetermined voltage from external measuring equipment to the first IDT electrode 11 via the wiring line 7, the first extraction electrode 19, and so forth.

Upon the voltage application, on the surface of the element substrate 10 a, the first IDT electrode 11-forming region is excited, thus producing SAW having a predetermined frequency. Part of the SAW so generated propagates toward the reaction section 13, passes through the reaction section 13, and reaches the second IDT electrode 12. In the reaction section 13, the aptamer on the reaction section 13 is bound to a specific object to be detected contained in the analyte liquid, and the weight (mass) of the reaction section 13 changes correspondingly, which results in variation in the characteristics, such as a phase, of the SAW passing through the reaction section 13. In response to the arrival of the SAW having varied characteristics at the second IDT electrode 12, a corresponding voltage is developed in the second IDT electrode 12.

The thereby developed voltage is outputted through the second extraction electrode 20, the wiring line 70, and so forth. By reading the output with external measuring equipment, it is possible to examine the properties and constituents of the analyte liquid.

In the sensor apparatus 100, capillarity is utilized to direct the analyte liquid to the reaction section 13.

Specifically, as described earlier, when the second cover member 2 is joined to the intermediate cover member 1A, as shown in FIG. 1, the flow channel 15 is defined, in the form of a narrow elongate pipe, on the lower surface of the second cover member 2. Thus, by setting, for example, the width or the diameter of the flow channel 15 at a predetermined value with consideration given to the type of the analyte liquid, the materials of construction of the intermediate cover member 1A and the second cover member 2, and so forth, it is possible to cause capillarity in the flow channel 15 in the form of a narrow elongate pipe. For example, the flow channel 15 has a width of 0.5 mm to 3 mm, and a depth of 0.1 mm to 0.5 mm. As shown in FIG. 1(b), the flow channel 15 has a downstream portion (extension) 15 b which is a portion extending beyond the reaction section 13, and, the second cover member 2 is formed with the air release hole 18 which is in communication with the extension 15 b. Upon admission of the analyte liquid into the flow channel 15, air present in the flow channel 15 is expelled out of the air release hole 18.

With such a pipe form capable of causing capillarity defined by the cover members including the intermediate cover member 1A and the second cover member 2, upon contact with the inlet port 14, the analyte liquid is drawn into the interior of the sensor apparatus 100 while passing through the flow channel 15. Thus, the sensor apparatus 100 has an analyte liquid suction mechanism built in itself, and is therefore capable of analyte liquid suction without using an instrument such as a pipette.

(Positional Relationship Between Flow Channel 15 and Detecting Element 3)

In this embodiment, while the analyte-liquid flow channel 15 has a depth of about 0.3 mm, the detecting element 3 has a thickness of about 0.3 mm, that is; as shown in FIG. 1(b), the depth of the flow channel 15 and the thickness of the detecting element 3 are substantially equal. Therefore, if the detecting element 3 is placed as it is on the upper surface of the first cover member 1, the flow channel 15 will be blocked. In this regard, in the sensor apparatus 100, as shown in FIGS. 1(b) and 5, the element placement section 5 is defined by the first cover member 1 on which the detecting element 3 is mounted, and the intermediate cover member 1A joined onto the first cover member 1. The detecting element 3 is housed in this element placement section 5 so that the analyte-liquid flow channel 15 will not be blocked. That is, the depth of the element placement section 5 is adjusted to be substantially equal to the thickness of the detecting element 3, and, the detecting element 3 is mounted inside the element placement section 5. Thereby, the flow channel 15 can be provided.

The detecting element 3 is secured to the bottom surface of the element placement section 5 by, for example, a die-bonding material composed predominantly of resin such as epoxy resin, polyimide resin, or silicone resin.

The end 19 e of the first extraction electrode 19 and the wiring line 7 are electrically connected to each other by a metallic narrow wire 27 formed of, for example, Au. The connection between the end 20 e of the second extraction electrode 20 and the wiring line 7 is made in a similar way. Means for connecting the wiring line 7 with the first and second extraction electrodes 19 and 20 is not limited to the metallic narrow wire 27, but may be of an electrically-conductive adhesive such as a Ag paste. Since a gap is left in the part where the wiring line 7 makes connection with each of the first and second extraction electrodes 19 and 20, it is possible to suppress damage of the metallic narrow wire 27 when bonding the second cover member 2 to the first cover member 1. Moreover, the first extraction electrode 19, the second extraction electrode 20, the metallic narrow wire 27, and the wiring line 7 are covered with the protective film 28. By covering the first extraction electrode 19, the second extraction electrode 20, the metallic narrow wire 27, and the wiring line 7 with the protective film 28, it is possible to suppress corrosion of these electrodes and the like.

As described heretofore, according to the sensor apparatus 100 in the embodiment, by placing the detecting element 3 in the element placement section 5 of the first cover member 1, it is possible to provide the analyte-liquid flow channel 15 extending from the inlet port 14 to the reaction section 13, and thereby allow the analyte liquid, which has been drawn into the apparatus through the inlet port 14 under capillarity for example, to flow to the reaction section 13. That is, even with use of the detecting element 3 having a certain thickness, since the sensor apparatus 100 has an analyte liquid suction mechanism built in itself, it is possible to provide a sensor apparatus 100 capable of directing an analyte liquid to the detecting element 3 efficiently.

<Manufacturing Process of Detecting Element>

The following describes a procedure in the making of the detecting element 3 provided in the sensor apparatus 100 according to the embodiment of the invention. FIG. 7 is a schematic view showing procedural steps for manufacturing the detecting element 3.

First, a quartz-made element substrate 10 a is washed. After that, on an as needed basis, an Al film is formed on the lower surface of the element substrate 10 a by RF sputtering technique (FIG. 7(a)).

Next, an electrode pattern is formed on the upper surface of the element substrate 10 a. In this step, a photoresist pattern 51 of image reversal type for electrode-pattern formation is formed by photolithography technique (FIG. 7(b)).

Next, a metallic layer 52 having a three-layer structure composed of Ti/Au/Ti layers is formed on each of a photoresist pattern 51-bearing part and a photoresist pattern 51-free part of the upper surface of the element substrate 10 a by electron-beam vapor deposition equipment (FIG. 7(c)).

Next, a Ti/Au/Ti electrode pattern 53 is formed by lifting off the photoresist pattern 51 using a solvent, followed by oxygen-plasma asking treatment (FIG. 7(d)). In this embodiment, the Ti/Au/Ti electrode pattern 53 constitutes, in addition to a pair of IDT electrodes 11 and 12, immobilization film 13 a, a reflector and mounting extraction electrodes 19 and 20. The pair of IDT electrodes 11 and 12 are disposed so as to face each other, and, one of them serves as a transmitter, whereas the other serves as a receiver.

Next, a protective film 28 is formed on the upper surface of the element substrate 10 a so as to cover the Ti/Au/Ti electrode pattern 53 by, for example, TEOS (Tetra Ethyl Ortho Silicate)-plasma CVD technique (FIG. 7(e)).

Next, a protective film 28 pattern is defined by first forming a positive photoresist 54 on the upper surface of the protective film 28, followed by etching of the protective film 28 using RIE equipment (FIG. 7(f)). Specifically, the positive photoresist 54 is formed on a part of the protective film 28 which covers the IDT electrodes 11 and 12 and part of the immobilization film 13 a, and, following the completion of etching of other part free of the photoresist 54 using the RIE equipment, the photoresist 54 is lifted off with use of a solvent, whereupon the protective film 28 pattern for covering the IDT electrodes 11 and 12 and part of the immobilization film 13 a is formed. Note that, by removing the protective film 28 from a photoresist 54-free part of the Ti/Au/Ti electrode pattern 53 by etching using the RIE equipment, and subsequently etching the outermost Ti layer of the electrode pattern, a part of the immobilization film 13 a which is not covered with the protective film 28 may be given a two-layer structure composed of Au/Ti layers. In consequence, the immobilization film 13 a having a two-layer structure composed of Au/Ti layers is located between the paired IDT electrodes 11 and 12. Given that the pair of IDT electrodes 11 and 12 and the immobilization film 13 a of Au/Ti two-layer structure are grouped into a set, then there are provided two sets on a single sensor, and, one of the two sets is used as a set for detection, whereas the other is used as a set for reference.

After that, the Al film 50 formed on the lower surface of the element substrate 10 a is removed with use of fluonitric acid.

An aptamer composed of a nucleic acid or a peptide is immobilized on the upper surface of the immobilization film 13 a to form the reaction section 13 (FIG. 7(g)).

In the manner as described heretofore, the detecting element 3 is formed.

Next, the element substrate 10 a is cut in a predetermined size by dicing (FIG. 7(h)). After that, separate detecting elements 3 obtained by cutting process are fixedly attached, at their back sides, onto a wiring-equipped glass epoxy mounting substrate (hereafter referred to as “mounting substrate”) corresponding to the first cover member 1 with use of an epoxy adhesive. Then, a Au narrow wire used as the lead wire 27 is set to provide electrical connection between the wiring line 7 connected to the terminal 6 disposed on the mounting substrate and the end 19 e, 20 e of the extraction electrode disposed on the detecting element 3 (FIG. 7(i)).

Following the completion of placement of the intermediate cover member 1A, the second cover member 2, and so forth, the sensor apparatus 100 according to an embodiment of the invention is formed.

The manufacturing process of the detecting element 3, as well as the manufacturing process of the sensor apparatus 100, is not limited to the aforestated procedure shown in FIG. 7, and it is thus possible to adopt any other manufacturing process that enables production of the element substrate 10 a whose upper surface is configured so that the region 10 a 2 where the reaction section 13 is located is lower than the regions 10 a 1 where the first IDT electrode 11 and the second IDT electrode 12 are located.

The invention is not limited to the embodiment thus far described, and may therefore be carried into effect in various forms.

Although the reaction section 13 in the aforestated embodiment has been illustrated as comprising the immobilization film 13 a and the aptamer immobilized on the upper surface of the immobilization film 13 a, the invention is not limited to the aptamer, and thus, as an alternative, a reactant which undergoes reaction with an object to be detected contained in an analyte liquid and causes variation in SAW characteristics before and after analyte passage through the reaction section 13 may be immobilized on the upper surface of the immobilization film 13 a. Moreover, for example, in the case where the object to be detected in the analyte liquid reacts with the immobilization film 13 a, the reaction section 13 may be composed solely of the immobilization film 13 a without using a reactant such as the aptamer. Moreover, a non-conductive film may be used as the immobilization film 13 a instead of a metallic film, and the aptamer may be immobilized on the upper surface of the non-conductive film.

Moreover, the detecting element 3 may be constructed of a single substrate on which a variety of devices are disposed. For example, an enzyme electrode for use with enzyme electrode method may be disposed next to a SAW device. In this case, in addition to measurement based on the immuno method using an antibody or aptamer, measurement based on the enzymatic method can also be conducted, thus increasing the number of measurement points that can be checked at one time.

Moreover, while the embodiment has been described with respect to the case of providing a single detecting element 3, a plurality of detecting elements 3 may be provided. In this case, the element placement section 5 is formed for each detecting element 3 on an individual basis, or, the element placement section 5 is configured to have a length or width large enough to receive all of the detecting elements 3.

Moreover, while the embodiment has been described with respect to the case where the first cover member 1, the intermediate cover member 1A, and the second cover member 2 are provided as separate components, this does not constitute any limitation, and thus either a combination of some of these members in an unitary structure or a combination of all the members in an unitary structure may be adopted.

REFERENCE SIGNS LIST

-   -   1: First cover member     -   1A: Intermediate cover member         -   1Aa: First upstream portion     -   2: Second cover member         -   2 a: Third substrate         -   2 b: Fourth substrate     -   3: Detecting element     -   4: Recess-forming area     -   5: Element placement section     -   6: Terminal     -   7: Wiring line     -   9: Filler member     -   10 a: Element substrate     -   10 b: Detecting section     -   11: First IDT electrode     -   12: Second IDT electrode     -   13: Reaction section         -   13 a: Immobilization film     -   14: Inlet port     -   15: Flow channel         -   15 a: Upstream portion         -   15 b: Downstream portion (extension)     -   18: Air release hole     -   19: First extraction electrode         -   19 e: End     -   20: Second extraction electrode         -   20 e: End     -   27: Lead wire (metallic narrow wire)     -   28: Protective film     -   100: Sensor apparatus 

The invention claimed is:
 1. A sensor apparatus, comprising: an element substrate; a detecting section disposed on and in direct contact with an upper surface of the element substrate, the detecting section comprising a reaction section having an immobilization film to detect an object to be detected, a first IDT electrode configured to generate an acoustic wave which propagates toward the reaction section, and a second IDT electrode configured to receive the acoustic wave which has passed through the reaction section, wherein the first and second IDT electrodes are located on the upper surface of the element substrate; and a protective film located on the upper surface of the element substrate so as to cover the first IDT electrode, the second IDT electrode, and a first part of the immobilization film, wherein a second part of the immobilization film is not covered by the protective film, the protective film extending between and contacting the immobilization film and at least one of the first IDT electrode and the second IDT electrode, and wherein, in an upper surface of the immobilization film, a region covered with the protective film is at a higher level than a region which is not covered with the protective film.
 2. The sensor apparatus according to claim 1, wherein the protective film covers the opposing ends of the immobilization film.
 3. The sensor apparatus according to claim 2, wherein the protective film covers the opposing ends of the immobilization film but does not cover a central region of the immobilization film located between the opposing ends.
 4. The sensor apparatus according to claim 1, wherein an upper surface of the immobilization film is inclined so that a level of the upper surface becomes lower as approaching from a region which is covered with the protective film to a region which is not covered with the protective film.
 5. The sensor apparatus according to claim 1, wherein a thickness of the immobilization film in a region which is covered with the protective film is greater than a thickness of the immobilization film in a region which is not covered with the protective film.
 6. The sensor apparatus according to claim 1, wherein a thickness of the immobilization film becomes smaller as approaching from a region which is covered with the protective film to a region which is not covered with the protective film.
 7. The sensor apparatus according to claim 1, wherein a region which is covered with the protective film in an upper surface of the immobilization film is at a same level as at least one of an upper surface of the first IDT electrode and an upper surface of the second IDT electrode.
 8. The sensor apparatus according to claim 1, wherein a region which is not covered with the protective film in an upper surface of the immobilization film is at a lower level than at least one of an upper surface of the first IDT electrode and an upper surface of the second IDT electrode.
 9. The sensor apparatus according to claim 1, wherein a surface roughness of a region on which the immobilization film is located in the upper surface of the element substrate is smaller than a surface roughness of an upper surface of the immobilization film.
 10. The sensor apparatus according to claim 1, wherein a surface roughness of a region which is not covered with the protective film in an upper surface of the immobilization film is greater than at least one of a surface roughness of an upper surface of the first IDT electrode and a surface roughness of an upper surface of the second IDT electrode.
 11. The sensor apparatus according to claim 1, wherein a surface roughness of a region which is covered with the protective film in an upper surface of the immobilization film is equal to a surface roughness of an upper surface of the first IDT electrode and a surface roughness of an upper surface of the second IDT electrode.
 12. The sensor apparatus according to claim 1, wherein a material of the immobilization film is a same as a material of the first IDT electrode and a material of the second IDT electrode.
 13. The sensor apparatus according to claim 1, wherein the protective film is located between the immobilization film and at least one of the first IDT electrode and the second IDT electrode.
 14. The sensor apparatus according to claim 1, wherein an end of the protective film located on a side of the immobilization film comprises a lower end part and an upper end part, the lower end part being closer to a center part of the immobilization film than the upper end part when viewed in a lateral section.
 15. The sensor apparatus according to claim 1, wherein an end of the protective film located on a side of the immobilization film comprises a lower end part and an upper end part, the end being inclined so that a distance between the end and a center part of the immobilization film becomes shorter as the end going from the upper end part to the lower end part when viewed in a lateral section.
 16. The sensor apparatus according to claim 1, wherein a thickness of the protective film is smaller than at least one of a thickness of the first IDT electrode and a thickness of the second IDT electrode.
 17. The sensor apparatus according to claim 1, wherein the protective film contacts side surfaces of the first and second IDT electrodes and contacts the upper surface of the element substrate between the detecting section and the first or second IDT electrodes. 